Various technologies are known which avoid congestion of a network due to an increase of the amount of traffic in a radio communication system. For example, when a network (for example, a base station) monitors the amount of traffic of a mobile station during communication and detects an amount of traffic exceeding a given value, the network changes the communication band (channel) currently used by the mobile station, or restricts the call from the mobile station. Optionally, a mobile station during communication in a cell compares the results of measurement of the received signal power from neighbor base stations with a threshold value indicated from the network. And when the received signal power from a neighbor cell of a base station exceeds the threshold value, handover to the cell of the neighbor base station is performed according to a control message from the network. A mobile station on standby in a cell compares the results of measurement of the received signal power from neighbor cells of base stations with a threshold value included in information for notice sent from the network. When the received signal power from a neighbor base station exceeds the threshold value, a cell for standby is changed (cell reselection) from the serving cell to the cell of the neighbor base station.
The following are reference documents: Japanese Laid-Open Patent Publication No. 2003-9209, Japanese Laid-Open Patent Publication No. 2008-288627, Japanese Laid-Open Patent Publication No. 2008-104190, and Japanese Laid-Open Patent Publication No. 2008-72291.